1. Field of the Invention
The present invention relates to an image-data processing system which may be used in an image forming apparatus. The system includes an electrophotographic system processing digital image data, such as an optical printer, a laser printer, a digital duplicator, a page-printing facsimile device, or an image display device. The present invention in particular relates to image fineness improvement in such an apparatus or system.
2. Related Art
An image forming device and an image display device quantize text image data or picture image data so that relevant data is expanded into a dot-matrix bit-map formation using two-tone data. The text image data is obtained by converting text code data using font data. The picture image data is read in using an image scanner or the like. The bit-map formation of the relevant data is stored in a video memory area in a RAM (random access memory) and is then read out sequentially to be supplied as video data to an image forming unit (engine) or to an image display unit. The image forming unit forms a corresponding image on a recording medium such as a sheet of paper or the like and the image display unit displays the corresponding image on a screen.
An ideal image is an analog image an outline of which may extend in a plurality of arbitrary directions. However, a bit-map image obtained as a result of quantization is a digital image an outline of which may extend only in two predetermined perpendicular dimensions of the dot matrix. Thus, an outline of a digital image representing an analog image having an outline extending obliquely or a curved manner can only extend stepwise along dot-matrix ruled lines (such a phenomenon may be referred to as `jag`) generally obliquely or generally in a curved manner. This property of the digital image may degrade fineness of the final image, thereby disabling precise representation of an original image or a desired outline.
Reduction in dot (pixel) size of the dot matrix, thereby increasing a number of dots present in a unit area (increasing a dot-matrix resolution), may reduce such image degradation. However, such resolution increase significantly raises the cost. For example, changing from a 300 dpi.times.300 dpi two-dimension bitmap to a 600 dpi.times.600 dpi one requires 4 times the memory capacity and 4 times the processing speed.
Other methods for reducing image degradation include an interpolation technology which is used to produce a line connecting consecutive corners present on a stepwise outline so as to form a slope therebetween. The interpolation technology can also be used to smooth brightness between adjacent outline dots so as to make an edge unclear. Such methods are effective to smooth jags on an outline but may degrade contrasts and/or resolution since fine shapes are made unclear.
In order to solve such a problem, a technology has been developed as disclosed in the U.S. Pat. No. 4,544,922. In this technology, a dot having a size smaller than an ordinary size is added or a partial area having the above smaller dot size is removed from an appropriate part of a dot pattern represented by a bit map so as to correct the relevant part. A pattern recognition technology or a template comparison technology is used to detect a part to be corrected in the dot pattern. The above disclosed technology performs the pattern recognition process or the template comparison process on all positions of a bit-map image and performs dot correction such as described above appropriately. As a result, although it is possible to improve image quality (image fineness) by smoothing a line shape without degrading contrasts, the relevant processing system is extremely costly and time-consuming.
In order to solve the problem, a method is proposed in Japanese Laid-Open Patent Application No.2-112966. In this method, a relevant bit-map image is compared with a previously stored predetermined template for each small fragment of an images. Then, if matching in characteristics is detected between the bit-map image and a template for an image fragment, the fragment of the bit-map image is corrected by correction dots. Thus, the image quality of a printed image is improved.
In order to realize the above method, a template matching process described below may be performed. Data of a bit map is converted into serial data so as to be input to a FIFO (first-in first-out) buffer. Then, a subset of a bit-map image of N.times.M bits is formed. A sample window is used to observe or extract therethrough data from the subset of the bit-map images. The sample window has a predetermined shape, a predetermined number of bits and a central bit corresponding to that of the subset image. Then, the thus observed or extracted data is used to detect matching with templates having various characteristic patterns which patterns are ones of images to be corrected.
If any template matches the observed or extracted data, a certain correction sample (correction dot) is used to replace the central bit in the relevant subset image. The correction sample corresponds to the relevant template. If no template matches the observed or extracted data, the relevant central bit is left unchanged.
Such template matching processes are performed by sequentially shifting the subset image to be processed so that all the area of the relevant bit-map image is processed. The processes are performed so that each bit of the bit-map image is assigned to be the above central bit sequentially. Thus, in comparison with the above technology disclosed in the U.S. Pat., a fine final image may be obtained by improving the image quality even with a relatively small memory capacity and with a relatively inferior data processing capability.
However, even in the above method, a great number of templates corresponding to all the characteristic patterns of images in the above sample-window formation are necessary. Producing the great number of templates requires considerable manpower and thus is costly. In addition, a considerable capacity of memory is required to store the templates. Further, the above-described template matching processes are time-consuming.
In order to solve the problems, the present applicant proposed a new image-data processing method and its device such as that disclosed in Japanese Laid-Open Patent Application No.5-207282.
The above method can eliminate jags such as described above so as to improve a resulting image quality using input image data in a bit-map formation. The method can reduce an amount of data stored in a memory, which data will be used to perform an appropriate correction process on the bit-map image. The method determines which dots in the input image data are to be corrected and which type of correction is required. The method carries out the above determination by means of simple logical operations in an extremely short time period using a microprocessor.
This method will now be briefly described. Characteristics of a line shape of a boundary between a black-dot region and a white-dot region in the bit map of input image data are recognized. As a result, the characteristics are then converted into a multi-bit code for each dot of the input image data. Then, at least a part of the code is used to determine whether or not the relevant dot is one to be corrected. Then, if the dot is determined to require correction, it is corrected in accordance with the relevant code. The above determination uses a pattern memory having addresses corresponding to the codes, wherein the appropriate correction may be determined according to the addresses.
Each multi-bit code includes a code indicating the slope (gradient) direction of the line at the position of the relevant dot, a code indicating the gradient of the slope, and a code indicating the position of the relevant dot. The above position is one, the origin of which is an initial dot in a series of dots straightly arranged vertically or horizontally and including the relevant dot.
In the above method, it is not necessary to provide and store as templates all characteristic patterns corresponding to ones to be corrected. Dots to be corrected and the correction required can be determined simply and within a short time period using the easily produced codes described above.
Further, dot data of dots present in an area, the center of which is the relevant dot, is extracted through an appropriate window. The area is separated into a core area located at the center and a plurality of peripheral areas located around the core area. The above code is produced based on recognition information obtained as a result of recognizing the line shape as mentioned above. The recognition information to be used to produce the code is a combination of core-area recognition information and peripheral-area recognition information. The core-area recognition information is obtained using the core area of the image data and the peripheral-area recognition information is obtained using at least one peripheral area of the image data. The at least one peripheral area is determined using the core area of the image data. Thus, it is possible to reduce the amount of information to be used in the production of the above codes so that the code production can be carried out efficiently.